Synergistic local anesthetic compositions

ABSTRACT

A local anesthetic composition comprising a mixture in a pharmaceutically acceptable carrier of a particular toxin, namely, tetrodotoxin or desoxytetrodotoxin, and another compound, generally a conventional local anesthetic compound or a similar compound having nerve-blocking properties.

This application is a continuation-in-part of our copending applicationSer. No. 206,181 filed Dec. 8, 1971, now abandoned which is acontinuation-in-part of Ser. No. 109,942 filed Jan. 26, 1971, nowabandoned.

The present invention relates to a novel anesthetic compositioncomprising a mixture of (1) tetrodotoxin or certain derivatives thereofand (2) another compound, generally a conventional local anestheticcompound, or a similar compound having nerve-blocking properties. Theinvention also relates to a process for preparing the novel anestheticcompositions and to their use for inducing anesthesia.

Toxins from marine sources of extraordinary potency have been known formany years. This application particularly concerns novel uses fortetrodotoxin.

Tetrodotoxin is obtained from the ovaries and eggs of several species ofpuffer fish of the suborder Gymnodontes. It is also found in certainspecies of California newts of the genus Taricha; and the toxin obtainedfrom these species, known as tarichatoxin, is identical withtetrodotoxin. Tetrodotoxin has been purified, and its molecularstructure is determined to be an amino perhydroquinazoline of theformula: ##SPC1##

Tetrodotoxin and species in which it occurs are more fully described inPharmacological Reviews, Vol. 18, No. 2, at pages 997-1049.

Experiments with isolated nerves have shown that tetrodotoxin behaves ina fundamentally different manner from local anesthetics such as procaineand cocaine. In a voltage-clamped giant axon from the squid or lobster,the latter agents reduce both inward initial sodium current and outwardpotassium current. With tetrodotoxin, however, inward sodium current canbe reduced or even obliterated, while the outward potassium current istotally unaffected. There are few, if any, other substances in whichthis unique action has been established.

Tetrodotoxin has not found any practical use as an anesthetic. While thecompound can be used to induce nerve blocks in laboratory animals, theanesthetic dose is slightly below the lethal dose, which precludes, as apractical matter the use of the compound as an anesthetic in its ownright.

Quite surprisingly, combinations of tetrodotoxin with a local anestheticcompound have been found to possess unusual anesthetic properties. Thisis manifested most significantly in improved longevity of action ofcombinations of the toxin with local anesthetics. In these combinations,tetrodotoxin is used in concentrations below that which producesreliable nerve blocks, and well below the toxic level.

Investigation of a wide variety of local anesthetics has shown that theaction of the foregoing toxin in increasing longevity of action isgeneral. Local anesthetics may be classified by characteristic chemicaltype. Within each chemical type there may be unexplained variations ofactivity. However, in all cases investigated, each member of the groupsinvestigated has behaved similarly when combined with the foregoingtoxin. Specific classes of local anesthetics investigated includeanesthetic compounds characterized by

i. the aminoacylanilide group, such as lidocaine, prilocaine,bupivacaine, mepivacaine and related local anesthetic compounds havingvarious substituents on the ring system or amine nitrogen;

The following three ester types (ii), (iii) and (iv):

ii. the aminoalkyl benzoate group, such as procaine, chloroprocaine,propoxycaine, hexylcaine, tetracaine, cyclomethycaine, benoxinate,butacaine, proparacaine, and related local anesthetic compounds;

iii. cocaine and related local anesthetic compounds;

iv. the amino carbamate group such as diperodon and related localanesthetic compounds;

v. the N-phenylamidine group, such as phenacaine and related localanesthetic compounds;

vi. the N-aminoalkyl amide group, such as dibucaine and related localanesthetic compounds;

vii. the aminoketone group, such as falicain, dyclonine and relatedlocal anesthetic compounds; and

viii. the aminoether group, such as pramoxine, dimethisoquine, andrelated local anesthetic compounds.

In each of the foregoing classes of local anesthetic compoundsrepresentative members have been enumerated. The experimental datasupport the conclusion that the observed effect of the toxin tested ofunexpectedly extending the duration of action extend to the other knownlocal anesthetic compounds of these groups and to the obviousmodifications of the local anesthetic compounds tested. It may also beanticipated in the light of these discoveries that the novelcombinations of the present invention will permit the use ofconcentrations of conventional local anesthetics in concentrations belowthe concentrations normally employed clinically. Thereby toxicmanifestations sometimes observed as side effects can be minimized.

The chemical structures of some of the foregoing compounds are: ##SPC2##

Other local anesthetic compounds which may be used in combination withthe tetrodotoxin (TTX) are the aminoacyl anilides described in thefollowing table.

                                      Table A                                     __________________________________________________________________________    Compound          R    R.sup.1                                                                            R.sup.2                                                                            R.sup.3                                      __________________________________________________________________________    A 2-tert. Butylamino-                                                           2',6'-acetoxylidide                                                                           H    H    H    C(CH.sub.3).sub.3                            B 2-(N-n-Butyl-tert. butylamino)-                                               2', 6'-acetoxylidide                                                                          H    H    n-C.sub.4 H.sub.9                                                                  C(CH.sub.3).sub.3                            C 2-(N-n-Propyl-tert. amylamino)-                                               2',6'-acetoxylidide                                                                           H    H    n-C.sub.3 H.sub.7                                                                  C(CH.sub.3).sub.2 C.sub.2 H.sub.5            D 2-tert. Butylamino-                                                           2',6'-propionoxylidide                                                                        H    CH.sub.3                                                                           H    C(CH.sub.3).sub.3                            E 2-(N-Ethyl-iso-propylamino)-                                                  2',6'-propionoxylidide                                                                        H    CH.sub.3                                                                           C.sub.2 H.sub.5                                                                    CH(CH.sub.3).sub.2                           F 2-Methylamino-4'-(n-butoxy)-                                                  2',6'-dimethylpropion-anilide                                                                 n-C.sub.4 H.sub.9 O                                                                CH.sub.3                                                                           H    CH.sub.3                                     G 2-(N-Methyl-n-propylamino)-                                                   2',6'-butyroxylidide                                                                          H    C.sub.2 H.sub.5                                                                    CH.sub.3                                                                           n-C.sub.3 H.sub.7                            H 2-Dimethylamino-                                                              2',6'-acetoxylidide                                                                           H    H    CH.sub.3                                                                           CH.sub.3                                     J 2-Ethylamino-2',6'-                                                           acetoxylidide   H    H    H    C.sub.2 H.sub.5                              K 2-Cyclobutylamino-2',6'-                                                      acetoxylidide   H    H    H                                                 L 2-tert. Amylamino-                                                            2',6'-acetoxylidide                                                                           H    H    H    C(CH.sub.3).sub.2 C.sub.2 H.sub.5            M 2-(N-Methyl-n-butylamino)-                                                    2',6'-acetoxylidide                                                                           H    H    CH.sub.3                                                                           n-C.sub.4 H.sub.9                            P 2-(N-Ethyl-sec. butylamino)-                                                  2',6'-acetoxylidide                                                                           H    H    C.sub.2 H.sub.5                                                                    CH(CH.sub.3)C.sub.2 H.sub.5                  Q 2-Amino-2',6'-propionoxylidide                                                                H    CH.sub.3                                                                           H    H                                            S 2-(N-Ethyl-n-propylamino)-                                                    2',6'-butyroxylidide                                                                          H    C.sub.2 H.sub.5                                                                    C.sub.2 H.sub.5                                                                    n-C.sub.3 H.sub.7                            T 2-Diethylamino-2',6'-                                                         valeroxylidide  H    n-C.sub.3 H.sub.7                                                                  C.sub.2 H.sub.5                                                                    C.sub.2 H.sub.5                              __________________________________________________________________________

In the present invention the foregoing local anesthetics are used in apharmaceutically acceptable carrier, such as water, water-ethanol,dextrose solutions, saline solution and blends thereof, inconcentrations which are customarily used by physicians. Exemplaryconcentrations of local anesthetics having clinical application are:

                          % by weight                                             ______________________________________                                        lidocaine                0.5 - 5                                              prilocaine               0.5 - 5                                              procaine                 0.5 - 5                                              tetracaine               0.1 - 1                                              bupivacaine             0.25 - 1                                              hexylcaine               0.5 - 2.5                                            2-[N-n-propyl-tert. amylamino]-                                               2',6'-acetoxylidide      0.1 - 2.0                                            2-[N-n-butyl-tert. butylamino]-                                               2',6'-acetoxylidide      0.1 - 2.0                                            ______________________________________                                    

As mentioned above, the present invention also may permit the use of theusual local anesthetics in a lower than normal concentration. Forexample, the combination of tetrodotoxin with lidocaine permits thelatter to be used in a concentration of as little as 0.05 percent byweight.

The carrier additionally contains from 0.5 to 10, usually from 0.5 to 5,micrograms per milliliter of tetrodotoxin or from 10 to 20 microgramsper milliliter of desoxytetrodotoxin. In addition, the local anestheticpreparation may contain a vascoconstrictor, as is well known in the art,such as epinephrine, norepinephrine, phenylephrine and levonordephrine.

The local anesthetic compositions may be prepared by dissolving thelocal anesthetic compound, tetrodotoxin or derivative thereof and avascoconstrictor, when present, in the carrier or in separate portionsof the carrier which are thereafter blended together.

Application of the local anesthetic compositions is accomplished in theusual manner, i.e., by infiltration or injection.

EXAMPLE 1

Female Charles River rats, weighing between 100 and 200 grams, wereused. There were 5 rats per group and each animal received 0.2milliliters of drug solution in the right thigh. The injections weremade in such a way as to deposit the solution around the sciatic nervetrunk close to the popliteal space. After being injected, each animalwas examined at intervals to determine onset, depth, and duration ofnerve block as manifested by impairment of motor function in theinjected leg. Frequencies of (a) complete block, (b) partial block, and(c) slight effect on motor function were noted for each group ofanimals. Two end points for duration of block were used: recovery of theability to grasp when placed on an inclined screen and complete recoveryof motor function.

All solutions contained 1 to 100,000 parts epinephrine which was addedimmediately prior to use. All solutions were freshly prepared on the dayof use.

The results are summarized in Tables I - III. Depression wasoccasionally noted, but there were no fatalities with these doses oftetrodotoxin.

Table I:

At 1 μg/ml and 2 μg/ml tetrodotoxin produced no complete blocks. At 5μg/ml, it produced complete blocks in all five legs injected. Mean onsettime was about 20 minutes, and the blocks persisted for somewherebetween 51/2 hours and 24 hours. All animals were completely recoveredwhen examined 22 to 24 hours post injection. Because this concentrationof tetrodotoxin by itself produced 100 percent frequency and blocks ofsuch long duration, there are no differences, except in onset times,between the results obtained with it alone and those obtained with thetetrodotoxin-lidocaine combination. However, the combinations of 1 μg/mland 2 μg/ml of tetrodotoxin with lidocaine clearly show durations ofblock that are markedly greater than those obtained with lidocainealone.

                                      TABLE I                                     __________________________________________________________________________    RAT SCIATIC NERVE BLOCKS                                                                                          Duration (min.)                                  Concentration                                                                             Onset                                                                              Frequency   Mean ± S. D.                           Compound                                                                              as Base                                                                              pH  (min.)                                                                             C   P   S   C.R.    R.G.                              __________________________________________________________________________    Tetrodotoxin                                                                          1 μg/ml                                                                           4.4 --   0/5 1/5 4/5 --      --                                        2 μg/ml                                                                           5.4 --   0/5 2/5 3/5 --      --                                        5 μg/ml                                                                           4.3 22   5/5 --  --  --      5.5<24 hrs.                       Lidocaine                                                                             0.125% 5.1 8    5/5 --  --  85 ± 2                                                                             84 ± 1.5                               0.25%  5.0 5    5/5 --  --  108 ± 22                                                                           99 ± 24                        Combinations                                                                   T/L    1/0.125                                                                              4.9 5.5  5/5 --  --  309 ± 17                                                                           251 ± 51                        T/L    2/0.125                                                                              4.8 5.0  4/5 1/5 --  316 ± 33                                                                           290 ± 46                        T/L    5/0.125                                                                              4.6 3.5  5/5 --  --  --      6<24 hrs.                          T/L    1.0.25 4.7 4.5  5/5 --  --  5.5<24 hrs.                                                                           299 (2)                            T/L    2/0.25 4.8 3.0  5/5 --  --  --      5.5<24 hrs.                        T/L    5/0.25 4.6 1.5  5/5 --  --  --      6<24 hrs.                         __________________________________________________________________________     Notes:                                                                        C = Complete block; P = Partial block; S = Slight effect; R.G. = Recovery     of grasping; C.R. = Complete Recovery; T = Tetrodotoxin; L 32  Lidocaine.     Durations are for complete blocks only. Onset times are approximate. The      pH's are after addition of epinephrine; all solutions contained 1:100,000     epinephrine. Numbers of blocks are in specific instances shown in             parentheses.                                                             

Table II:

As in the first study, 1 μg/ml of tetrodotoxin produced no completeblocks; however, 2 μg/ml produced a complete block, with a duration ofabout 2 hours, in one out of five injections. The frequency of blockwith 3 μg/ml was only two out of five, but the block persisted forbetween 5 and 24 hours. In this study lower concentrations of lidocainewere used in order to ascertain whether or not the combinations showbetter frequencies than either tetrodotoxin or lidocaine alone.

                                      TABLE II                                    __________________________________________________________________________    RAT SCIATIC NERVE BLOCKS                                                                                          Duration (min.)                                  Concentration                                                                             Onset                                                                              Frequency   Mean ± S. D.                           Compound                                                                              as Base                                                                              pH  (min.)                                                                             C   P   S   C.R.    R.G.                              __________________________________________________________________________    Tetrodotoxin                                                                          1 μg/ml                                                                           4.6 --   0/5 0/5 5/5 --      --                                        2 μg/ml                                                                           4.7 31   1/5 0/5 4/5 120     102                                       3 μg/ml                                                                           4.5 56   2/5 0/5 3/5 --      5<24 hrs.                         Lidocaine                                                                             0.05%  4.6 --   0/5 2/5 3/5 --      --                                        0.1%   4.6 43   2/5 2/5 1/5  58     44                                Combinations                                                                   T/L    1/0.05 4.6 31   1/5 2/5 2/5  68     48                                 T/L    2/0.05 4.4 10   2/5 2/5 1/5 255     176                                T/L    3/0.05 4.5 16   3/5 2/5 --  61/2<24 hrs.                                                                          359 ± 42                        T/L    1/0.1  4.5 11   2/5 3/5 --  144     93                                 T/L    2/0.1  4.6  6   4/5 0/5 1/5 242 ± 68                                                                           188 ± 83                        T/L    3/0.1  5.2 14   4/5 1/5 --    304 (1)                                                                             317 ±50                                                            61/2<24 hrs.                                                                          (3)                               __________________________________________________________________________     See Notes under Table I.                                                 

Table III:

Tetrodotoxin at 3 μg/ml produced in three out of five animal blocks thatlasted between 4 and 24 hours. In combinations with several localanesthetic agents, frequency was improved and onset times were shorterthan with tetrodotoxin alone. All the combinations containing 1 μg/ml oftetrodotoxin exhibited durations of block much greater than obtainedwith the local anesthetic agents alone. The study clearly demonstratesthat, in rat sciatic nerve blocks, the presence of concentrations oftetrodotoxin that by themselves are subthreshhold can cause markedincreases in the durations of block of several local anesthetic agents.

                                      TABLE III                                   __________________________________________________________________________    RAT SCIATIC NERVE BLOCKS                                                                                          Duration (min.)                                  Concentration                                                                             Onset                                                                              Frequency   Mean ± S. D.                           Compound                                                                              as Base                                                                              pH  (min.)                                                                             C   P   S   C.R.     R.G.                             __________________________________________________________________________    Tetrodotoxin                                                                          1 μg/ml                                                                           4.6 --   0/5 1/5 4/5 --       --                                       3 μg/m.                                                                           4.3 48   3/5 2/5 --    4<24 hrs.                               Lidocaine                                                                             2.0%   4.4 2.0  5/5 --  --  172 ± 17                                                                            160 ± 12                       T/L    1/2.0  4.5 1.5  5/5 --  --  223 (2)  188 (2)                                                                41/2<24 hrs.                                                                         (3)                               T/L    3/2.0  4.3 1.5  5/5 --  --    41/2<24 hrs.                            Bupivacaine                                                                           0.5%   5.0 2.5  5/5 --  --  232 ± 39                                                                            183 ± 18                       T/B    1/0.5  5.2 6.0  5/5 --  --  282 (2)  265 ± 45                                                          5<24 hrs.                                                                              (3)                                T/B   3/0.5  5.4 2.5  5/5 --  --    5<24 hrs.                               Prilocaine                                                                            2.0%   5.0 2.5  5/5 --  --  153 ± 16                                                                            123 ± 6                        T/Pr   1/2.0  4.8 <1.0 5/5 --  --  5<24 hrs.                                                                              251 ± 26                       T/Pr   3/2.0  4.8 2.0  5/5 --  --   °5<24 hrs.                        Tetracaine                                                                            0.25%  5.2 4.0  3/5 2/5 --  206 (2)  180 (2)                                                                41/2<24 hrs.                                                                         (1)                               T/Tet  1/0.25 5.9 5.5  4/5 1/5 --   4<24 hrs.                                 T/Tet  3/0.25 6.4 5.0  5/5 --  --   3<24 hrs.                                __________________________________________________________________________     See Notes under Table I.                                                      B = Bupivacaine; Pr = Prilocaine; Tet = Tetracaine.                      

EXAMPLE 2

The use of anesthetics of the present invention is also shown throughperidural blocks in the cat. The surgical techniques and testing methodshave been described in detail (Duce et al: Brit. J. Anaesth., Vol. 41,579-587 (1969)). The animals were treated according to the followingscheme in this study:Cat Weight Day (treatment)No. and Sex 1 2 3 45______________________________________124 3.6 kg F X L TTX L/TTX X1252.8 kg F X L L/TTX TTX X127 4.0 kg M X TTX L L/TTX X128 2.8 kg F X TTXL/TTX L X______________________________________ X = Xylocaine HCl, 2% assalt L = Lidocaine HCl, 2% as base TTX = Tetrodotoxin, 1 μg/ml F =female M = male

All animals were tested with 2 percent Xylocaine (a commercial localanesthetic composition based on lidocaine as the active ingredient) onDays 1 and 5 to ascertain the stability of the peridural catpreparation. Within the test period, laboratory-prepared samples oflidocaine were used containing only lidocaine and epinephrine orlidocaine, epinephrine and tetrodotoxin in specified proportions.Solutions were freshly prepared each day of use; epinephrine was addedand the pH taken shortly after administration The pH's of the solutionswere: tetrodotoxin, 4.5-6.75; lidocaine HCl, 1, 4.75-4.8;lidocaine/tetrodotoxin, 4.75-4.9.

The results are summarized in Table IV. In general, no overt systemiceffects were noted following administration of the test solutions.Animal No. 127 exhibited salivation and emesis, with bile present, about3 hours and 45 minutes after administration of thelidocaine/tetrodotoxin combination. However, these observations were notconsidered significant.

Statistical analysis of the data showed that the Xylocaine controlvalues obtained on days 1 and 5 are not significantly different. Sincetetrodotoxin alone produced no blocks, it was excluded from the analysisof variance in order to keep the variance reasonably homogeneous. Afour-way analysis of variance was, therefore, done only with the dataobtained with 2 percent lidocaine and with the lidocaine/tetrodotoxincombination. The durations of block with the lidocaine tetrodotoxincombination were statistically significantly longer than with lidocaineitself.

                                      TABLE IV                                    __________________________________________________________________________    PERIDURAL ANESTHESIA IN CAT                                                               Deep Motor Block                                                                              Block of Support of Weight                                                                     Block of Flexion Reflex          Compound and                                                                              Duration        Duration         Duration                         Concentration                                                                             x ± S.E.                                                                         Onset                                                                             Frequency                                                                           x ± S.E.                                                                          Onset                                                                             Frequency                                                                           x ± S.E.                                                                          Onset                                                                             Frequency             __________________________________________________________________________    2% Xylocaine (Day 1)                                                                      119 ± 12                                                                          1  8/8   98 ± 13                                                                           <1  8/8   48 ± 10                                                                           8   4/8                   2% Xylocaine (Day 5)                                                                      124 ±0 11                                                                        1-2 8/8   106 ±  9                                                                          1   8/8   70 ± 17                                                                           7   6/8                   1 μg/ml Tetrodotoxin                                                                   --    --  0/8   --     --  0/8   --     --  0/8                   2% Lidocaine                                                                              115 ± 10                                                                         2-3 8/8   88 ± 10                                                                           2   8/8   66 ± 19                                                                           7   5/8                   Lidocaine/tetrodotoxin                                                                    226 ±  9                                                                         <1  8/8   188 ±  9                                                                          <1  8/8   109 ±  8                                                                          7   7/8                   __________________________________________________________________________     Durations are in minutes.                                                     Mean onset times are approximate.                                             Durations of block of flexion reflex in this table were calculated withou     zero values.                                                                  All solutions contained 1:100,000 epinephrine.                           

EXAMPLE 3

The effectiveness of the local anesthetics of the present invention inthe absence of epinephrine is shown by the data set forth in Tables V,VI and VII. The data summarized in these tables were obtained followingthe same procedures as described in Example 1.

Five separate studies were done, and a tetrodotoxin control group wasrun in each study. Frequency of block with tetrodotoxin ranged from 0/5to 3/5, and durations ranged from about 180 to 240 minutes. Frequency ofblock was 5/5 with all combinations except that containing phenacaine(Table VI). The one partial block in this case may have been due tofailure to inject the solution sufficiently close to the sciatic nervetrunk. The frequency of block with the diperodon-tetrodotoxin,cyclomethycaine-tetrodotoxin and dibucaine-tetrodotoxin were better thanwith diperodon, cyclomethycaine, dibucaine or tetrodotoxin by itself.

In all cases, the combinations produced durations markedly longer thanobtained with the local anesthetics alone. The durations of tetrodotoxinalone were closer to those with the combinations; the frequencies wereconsistently lower than those produced by the combinations.

                                      TABLE V                                     __________________________________________________________________________    RAT SCIATIC NERVE BLOCKS                                                                                        Duration (min.)                                        % Conc.   Onset                                                                              Frequency                                                                             Mean ± S. D.                             Compound   as base                                                                             pH  (min.)                                                                             C   P   C.R.  R.G.                                  __________________________________________________________________________    Lidocaine  2.0   4.8 1    5/5 --  108 ± 48                                                                         103 ± 37                           Lidocaine/TTX                                                                            2.0   4.8 <1   5/5 --  385 ± 25                                                                         348 ± 17                           Procaine   2.0   5.5 2.5  5/5 --   62 ±  7                                                                          60 ±  7                           Procaine/TTX                                                                             2.0   5.5 2    5/5 --  356 ± 53                                                                         314 ± 58                           Chloroprocaine                                                                           2.0   5.4 1.5  5/5 --  111 ± 65                                                                          87 ± 36                           Chloroprocaine/TTX                                                                       2.0   5.3 1    5/5 --  351 ± 73                                                                         325 ± 46                           Tetrodotoxin                                                                             2 μg/ml                                                                          6.0 13   2/5 0/5 242 ±  4                                                                         226 ±  5                           Diperodon  0.25  5.4 22   2/5 0/5 124    64                                   Diperodon/TTX                                                                            0.25  5.4 9    5/5 --  332 ± 59                                                                         286 ± 33                           Propoxycaine                                                                             0.25  5.4 4    5/5 --   64 ± 12                                                                          52 ± 15                           Propoxycaine/TTX                                                                         0.25  5.5 1.5  5/5 --  262 ± 91                                                                         239 ± 102                          Hexylcaine 0.5   5.6 3    5/5 --  112 ± 12                                                                          99 ± 17                           Hexylcaine/TTX                                                                           0.5   5.5 4.5  5/5 --  339 ± 17                                                                         303 ± 12                           Cocaine    0.25  6.1 4.5  5/5 --   98 ±  9                                                                          86 ± 17                           Cocaine/TTX                                                                              0.25  5.6 5    5/5 --  (1 day)                                                                             361 ± 28                           Tetrodotoxin                                                                             2 μg/ml                                                                          6.1 16   2/5 1/5 216 ± 51                                                                         161                                   __________________________________________________________________________     TTX = Tetrodotoxin, 2 μg/ml;                                               C = Complete block;                                                           P = Partial block;                                                            C.R. = Complete recovery of normal motor function;                            R.G. = Recovery of grasping;                                                  Durations are for complete blocks                                             Onset times are approximate.                                             

                                      TABLE VI                                    __________________________________________________________________________    RAT SCIATIC NERVE BLOCKS                                                                                       Duration (min.)                                        % Conc.   Onset                                                                              Frequency                                                                             Mean ± S. D.                              Compound  as base                                                                             pH  (min.)                                                                             C   P   C.R.  R.G.                                   __________________________________________________________________________    Phenacaine                                                                              0.25  5.6 4.5  5/5 --   78 ± 32                                                                          70 ± 32                            Phenacaine/TTX                                                                          0.25  5.5 8    4/5 1/5 282 ± 74                                                                         253 ± 71                            Benoxinate                                                                              0.25  5.6 3    5/5 --  116 ± 24                                                                          97 ± 20                            Benoxinate/TTX                                                                          0.25  5.6 8    5/5 --  320 ± 54                                                                         285 ± 58                            Butacaine 0.25  5.8 6    4/5 1/5  73 ±  7                                                                          67 ±  2                            Butacaine/TTX                                                                           0.25  5.6 5    5/5 --  241 ± 24                                                                         204 ± 37                            Tetrodotoxin                                                                            2 μg/ml                                                                          6.1 18   1/5 --  181   150                                    Proparacaine                                                                            0.5   6.0 1.5  5/5 --   98 ± 20                                                                          89 ± 14*                           Proparacaine/TTX                                                                        0.5   6.1 2    5/5 --  429 ± 41                                                                         415 ± 50*                           Tetrodotoxin                                                                            2 μg/ml                                                                          6.2 13   3/5 2/5 222 ± 48                                                                         206 ± 42                            __________________________________________________________________________     TTX = Tetrodotoxin, 2 μg/ml;                                               C = Complete block;                                                           P = Partial block;                                                            C.R. = Complete recovery of normal motor                                      R.G. = Recovery of grasping;                                                  Durations are for complete blocks                                             Onset times are approximate.                                                  *Means of 3 animals; 2/5 died.                                           

                                      TABLE VII                                   __________________________________________________________________________    RAT SCIATIC NERVE BLOCKS                                                                                        Duration (min.)                                         % Conc.   Onset                                                                             Frequency                                                                             Mean ±  S.D.                             Compound    as base                                                                             pH  (min.)                                                                            C   P   C.R.  R.G.                                  __________________________________________________________________________    Cyclomethycaine                                                                           0.125 5.1 17  1/5 4/5 145   115                                   Cyclomethycaine/TTX                                                                       0.125 5.2 5   5/5 --  273 ± 43                                                                         231 ± 41                           Dibucaine   0.125 5.4 6   3/5 1/5 125 ± 22                                                                         108 ± 25                           Dibucaine/TTX                                                                             0.125 5.4 6   5/5 --  324 ± 47                                                                         272 ± 56                           Tetrodotoxin                                                                              2 μg/ml                                                                          5.6 --  0.5 1/5   --    --                                  __________________________________________________________________________     TTX = Tetrodotoxin, 2 μg/ml;                                               C = Complete block;                                                           P = Partial block;                                                            C.R. = Complete recovery of normal motor                                      R.G. = Recovery of grasping;                                                  Durations are for complete blocks                                             Onset times are approximate.                                             

EXAMPLE 4

The use of desoxytetrodotoxin was tested following the proceduredescribed in Example 1. The desoxy derivative was substituted for thetetrodotoxin referred to in Example 1. Desoxytetrodotoxin was tested,without epinephrine, in rat sciatic nerve blocks. At concentrations of5, 10 and 20 μg/ml it produced no blocks. The duration of block of acombination containing 2 percent lidocaine and 5 μg/ml ofdesoxytetrodotoxin was not significantly different from that of 2percent lidocaine alone. However, combinations containing 10 and 20μg/ml of desoxytetrodotoxin produced blocks that were significantlylonger (1.4-1.6 times) than that of lidocaine alone (0.008 > p > 0.016).

This result is to be expected based on the tests of tetrodotoxin in viewof the lower activity shown by the desoxy derivative in toxicity tests.Literature on the toxicity of tetrodotoxin and its desoxy derivativereports the latter to be between one quarter and one tenth as toxic asits parent toxin.

EXAMPLE 5

Method: Mature male beagles are surgically prepared by implantation of acannula into a lumbar vertebra so that drug solutions may beadministered into the peridural space. After administration of localanesthetic solutions, the animals are examined at intervals for durationof loss of pain in the scrotal area and in the digits of the hind limbsas well as for loss of ability to support their weight.

Response to and awareness of pain stimuli in scrotal areas is a test foranesthetic block in spinal roots L3-4 and S1-2-3. These roots are thefurthest removed from the point of injection (L6) and, therefore, leastlikely to be affected by the anesthetic. Return of response to pain inthe scrotum is often the first sign of recovery and indicates recessionof anesthesia to at least L4 anteriorly and S2 posteriorly.

                                      TABLE VIII                                  __________________________________________________________________________    PERIDURAL ANESTHESIA IN DOGS                                                          Onset:  mean and range                                                                       Duration:  mean and range                              Compound and                                                                          Digital                                                                            Scrotal                                                                            Weight                                                                             Digital                                                                             Scrotal                                                                             Weight                                     Concentration                                                                         Pain Pain Support                                                                            Pain  Pain  Support                                    __________________________________________________________________________    Lidocaine 2%                                                                          7    8    <5   127   111   137                                        (n=3)                  76-162                                                                              62-152                                                                              108-162                                    Tetrodotoxin                                                                          19.5 15*  <17  225         406                                        4 μg/ml                                                                    (n=2)   19-20          87-350                                                                               0-125                                                                              339-473                                    Lidocaine 2%           316   301   462                                        Tetrodotoxin                                                                          <5   <5   <3   245-387                                                                             235-367                                                                             400-525                                    4 μg/ml                                                                    (n=2)                                                                         __________________________________________________________________________     *One animal only; no anesthesia in second animal.                             Onsets and durations are in minutes.                                          All Solutions contained 1:100,000 epinephrine.                                Volume of administration = 5 ml.                                              n = number of animals                                                         NOTE*                                                                         (1) With lidocaine onset is rapid, frequency of block is 100%, but            durations are short.                                                          (2) With tetrodotoxin durations are long, but onset is slow and frequency     of block of scrotal pain is poor.                                             (3) With the combination onset is rapid, frequency is 100% and durations      are long.                                                                

EXAMPLE 6

Following the method described in Example 1 above, various localanesthetic compounds alone, TTX alone and combinations of the compoundswith TTX were tested for their ability to block the rat sciatic nerve.TTX was used uniformly in the amount of 2 μg/ml. Each of thecompositions tested contained epinephrine in concentration of 1:100,000.The results are presented in Table IX. In the case of compound A in 0.5percent concentration, duration was about 126 minutes. TTX alone wasabout 295 minutes but frequency was not good. In combination, frequencywas good and duration was greater than 420 minutes.

In the case of compound D at 0.25 percent concentration, duration wasabout 128 minutes alone but greater than 420 minutes in combination withTTX. In the case of compound E at 0.25 percent concentration, no blockswere observed alone, but in combination with TTX the duration was about148 minutes. In the case of compound F alone at 0.125 percentconcentration, duration was only 78 minutes with poor frequency, whereasin combination with TTX duration was greater than 322 minutes andfrequency had improved. For compound G at 0.5 percent concentration,duration was 104 minutes alone and about 286 minutes in combination withTTX.

It should be noted moreover that in the case of TTX alone, frequencyfreqeuency and duration were quite variable ranging from zero frequencyto 4 out of 5, and ranging from zero duration to 295 minutes or more.

                  Table IX                                                        ______________________________________                                        Rat Sciatic Nerve Blocks                                                      Tetrodotoxin (TTX) (2 μg/ml) and Various Local Anaesthetic                 Compounds. Epinephrine concentration 1:100,000.                               Compound      Frequency  Duration (min.)                                                               Mean ± S.D.                                       ______________________________________                                        TTX           2/5         295*                                                A (0.5%)      5/5         126 ±12                                          TTX + A (0.5%)                                                                              5/5        >420, <24 hrs.**                                     A (1.0%)      5/5         157 ± 18                                         TTX + A (1.0%)                                                                              5/5        >420, <24 hrs.                                       TTX           4/5         316 ± 10*                                        D (0.25%)     5/5         128 ± 13                                         TTX + D (0.25%)                                                                             5/5        >420, <24 hrs.                                       D (0.5%)      5/5         133 ± 7                                          TTX + D (0.5%)                                                                              5/5        >420, <24 hrs.                                       TTX           0/6           0                                                 E (0.25%)     0/6           0                                                 TTX +E (0.25%)                                                                              4/6         148 ± 27                                         TTx           0/5           0                                                 F (0.125%)    1/5          78                                                 TTX + F (0.125%)                                                                            3/5        >322 min.                                            TTX           0/5           0                                                 G (0.5%)      5/5         104 ± 14                                         TTX + G (0.5%)                                                                              4/5         286 ± 197                                        ______________________________________                                          *One animal blocked >420 min.                                                **> 420, <24 hrs. means that the animals returned to normal during a          period when they were not observed, this period being longer than 7 hrs.      and shorter than 24 hrs.                                                 

EXAMPLE 7

In vitro tests were made on the isolated intact frog sciatic nerve usingcompounds B, C and lidocaine alone and in combination with TTX. Theresults and the method followed are presented in Table X. The reductionin the action potential of compound B alone was 22 percent and for TTXalone it was 15 percent, as compared with a reduction of 94 percent forthe combination. For compound C alone the reduction was 24 percent, andfor TTX alone 29 percent, whereas the combination again reduced thepotential by 94 percent. For lidocaine and TTX each alone the reductionswere 15 and 7 percent, respectively, as compared with a reduction of 61percent for the combination of the two.

                  Table X                                                         ______________________________________                                        Block of Isolated Intact Frog Sciatic Nerve.                                  Compound                                                                              pH     Concn.   Percent reduction                                                                         Number of                                                mM       of the action                                                                             experiments                                                       potential.                                                                    Mean and range                                        ______________________________________                                        B       5.6    0.625    22   (10-38)  16                                      TTX     5.6    3.sup.. 10.sup.-4                                                                      15   (8- )    17                                      B + TTX 5.6    as above 94    (80-100)                                                                              17                                      C       5.6    0.156    24   (15-52)  8                                       TTX     5.6    3.sup.. 10.sup.-4                                                                      29    (14-80*)                                                                              6                                       C + TTX 5.6    as above 94    (78-100)                                                                              12                                      Lidocaine                                                                             7.0    0.625    15    (6-30)  6                                       TTX     7.0    1.sup.. 10.sup.-4                                                                       7    (2-12)  6                                       Lidocaine                                                                             7.0    as above 61    (20-100)                                                                              12                                      + TTX                                                                         ______________________________________                                         *Occasionally a high value is observed, probably caused by a minute damag     to the nerve sheath during dissection. It takes about 50 times the            concentration of TTX which is necessary to block a desheathed nerve in        order to obtain the same degree of block of an intact (sheathed) nerve.  

Method: The method is essentially as described by A. P. Truant, Arch.Int. Pharmacodyn. 115, 483-497 (1958).

Sciatic nerve trunks of Rana pipiens are prepared by dissecting thenerve from its roots in the spinal cord to the ankle and placing it onsilver-silver chloride electrodes so that stimulation and recording ofthe action potential can be performed during the course of applicationof the test compounds and during the recovery period. The bathingsolution is Tasaki Ringer's. The observations lasted for 40 minutesallowing the action potentials to reach essentially a stable value(equilibrium).

EXAMPLE 8

Using the procedure described in Example 1 above, the effect of severalknown vasoconstrictors on rat sciatic nerve blocks was investigatedusing lidocaine (0.125 percent) and tetrodotoxin (2 μg/ml) incombination. The results are given in Table XI. Without anyvasoconstrictors, the frequency was very poor and the duration of blockwas 174 minutes. With phenylephrine, levonordefrin, or epinephrine,however, frequency was greatly improved and duration had about doubled.

                  Table XI                                                        ______________________________________                                        Effect of Vasoconstrictors on Rat Sciatic Nerve Blocks                        Obtained with Lidocaine (0.125%) and Tetrodotoxin (2 μg/ml).               Vasoconstrictor                                                                          Concn.      Frequency Duration of                                                                   Block (min.)                                                                  Mean ± S.D.                               ______________________________________                                        None       --          1/5       174                                          Phenylephrine                                                                            1:20,000    5/5       377 ± 27                                  Levonordefrin                                                                            1:20,000    5/5       354 ± 12                                  Epinephrine                                                                              1:200,000   5/5       368 ± 24                                  ______________________________________                                    

EXAMPLE 8a

Using the procedure described in Example 1, except that no epinephrinewas added to the solutions tested, the local anesthetics falicain andpramoxine were tested for blockage on the rat sciatic nerve alone and incombination with TTX at 2 μg/ml. The results are presented in thefollowing Table XII.

                  TABLE XII                                                       ______________________________________                                        Rat Sciatic Nerve Blocks                                                                  Frequency  Duration                                               ______________________________________                                        0.25% falicain                                                                              5/5          55 ± 22                                         0.25% falicain                                                                ± TTX, 2 μg/ml                                                                        5/5          116 ± 71                                        0.25% pramoxine                                                                             0/5          0                                                  0.25% pramoxine                                                                             2/5          190 ± 76                                        ± TTX, 2 μg/ml                                                          TTX, 2 μg/ml                                                                             0.5          0                                                  ______________________________________                                    

It will be observed that the ingredients were tested at dose level thatdid not result in any anesthesia at all for two of them, and only 55min. for the third one, whereas the combination gave anesthesia about 2to 3 hrs. The frequency of complete block was raised from 0 to 40percent in the case of pramoxine.

Compounds A, B, C, D and L described in Table A above are made by theprocedure described in U.S. Pat. application Ser. No. 369,146 filed June12, 1973 which is a continuation-in-part of Ser. No. 325,378, filed Jan.22, 1973, now abandoned both assigned to the same assignee as thepresent application, which disclosure is incorporated herein byreference.

The method of preparing compounds S and T is disclosed in U.S. Pat.application Ser. No. 164,022 filed July 19, 1971, now U.S. Pat. No.3,812,147 which is incorporated herein by reference.

The method of preparing compound Q is disclosed in U.S. Pat. applicationSer. No. 321,590 filed Jan. 8, 1973 now abandoned which is incorporatedherein by reference.

Compounds H, J and M and mepivacaine are known compounds disclosed inthe published literature.

EXAMPLE 9 Synthesis of 2-(N-ethyl-isopropylamino)-2',6'-propionoxylidide (Compound E)

A mixture of 12.81 g (0.050 mole) of 2-bromo-2',6'-propionoxylidide,11.31 g (0.130 mole) ethyl-isopropylamine and 30 ml dry toluene washeated in a glass-lined, stainless-steel pressure vessel at 105° for 20hours. After cooling to 25°, the brown reaction mixture was filtered,extracted three times with a total of 50 ml of 3 N HCl. The aqueoussolution was heated to 75° for ten minutes with decolorizing carbon andthen filtered. To the chilled solution was added 10 ml concentrated NH₃.The product which precipitated was filtered, washed, and dried. Yield:6.93 g (52.9%) m.p. 50°-2°.

Anhydrous ethereal HCl was added to 6.90 g of the above base dissolvedin 100 ml dry ether until the solution was acidic to moist pH paper,giving 6.15 g of tacky brown material, m.p. 191°-201°. The hydrochloridewas recrystallized from a mixture of butanone and alcohol. Yield: 6.02g, m.p. 207.5°-209°.

Analysis: Calc'd. for C₁₆ H₂₇ ClN.sub. 2 O: C 64.30, H 9.11, N 9.37, Cl11.86. Found: C 64.16; H 9.16, N 9.49, Cl 12.09.

EXAMPLE 10 A. Synthesis of 2-Bromo-4'-butoxy-2',6'-dimethylpropionanilide

To a chilled (ca 10°) solution of 50.7 g (0.263 mole) of4-butoxy-2,6-dimethylaniline [Buchi et al., Helv. Chim. Acta, 34, 278(1951)] in 224 ml glacial acetic acid was added rapidly 62.4 g (.289mole) of 2-bromo-propionyl bromide and immediately thereafter a chilled(ca 5°) solution of 87.2 g sodium acetate trihydrate in 362 ml water.This mixture was shaken for 1/2 hour, filtered, washed with water untilthe washes were neutral, and dried in vacuo over silica gel and KOH;yield 68.9 g (71.6%); m.p. 132.5° - 133.5°. The product wasrecrystallized from 95% ethanol; m.p. 135.5° - 136°.

Analysis: Calc'd for C₁₅ H₂₂ NO₂ Br : C 54.87, H 6.76, Br 24.34. Found:C 55.06, H 6.22, Br 24.69.

B. Synthesis of 2-Methylamino-4'-butoxy-2',6'-dimethyl-propionanilide(Compound F)

To a cold stirred solution of 14.8 g. of monomethyl amine in 250 ml drybenzene was added (portionwise, keeping temperature below 10°), 19.5 g(0.0594 mole) of 2-bromo-4'-butoxy-2',6'-dimethyl propionanilide (madeaccording to the procedure in the first part of this example); thisdissolved readily, forming a clear solution. The mixture was heated to70° for ca 1 hr. with stirring, at which point a white precipitate hadseparated and reflux became so vigorous that the reaction had to becontrolled by external cooling.

The precipitated methylammonium bromide was filtered off. Excess amineand solvent were removed in vacuo from the filtrate, giving a whiteresidue which was dissolved in 120 ml 0.5 M HCl and filtered. Thefiltrate was extracted with 3 × 25 ml. ether; and the ether extractsdiscarded.

The aqueous phase was alkalized to pH 11, and extracted with ether; thecombined extracts were dried (Na₂ SO₄), filtered, and evaporated, givinga yield of 8.7 g (52.7%); m.p. 107°-107.5°. Recrystallization fromcyclohexane did not affect the melting point.

Analysis: Calc'd. for C₁₆ H₂₆ N₂ O₂ : C 69.0; H 9.41; N 10.06. Found: C69.0; H 9.17; N 10.06.

EXAMPLE 11 Synthesis of 2-(N-Methyl-n-propylamino)-2',6'-butyroxylidide(Compound G)

To a stirred solution of N-methyl-n-propylamine (9.10 g, 0.125 mole) in175 ml of anhydrous benzene was added 2-iodo-butyro-2',6' -xylidide(13.2 g, 0.0415 mole). The mixture was allowed to reflux for 5 hrs.

The reaction mixture was extracted with 1 M HCl. After filtration toremove trace insolubles, the pH was adjusted to 9 with 7 M NaOH, whichcaused the formation of a light-yellow waxy solid. The latter wasfiltered, washed with water, and dried; yield 4.00 g (36.7%).

This base was converted to the hydrochloride salt with ethereal HCl. Thehydrochloride was twice-recrystallized from ethanol/ether, affordingcrystals melting at 214°-215°C.

Analysis: Calc'd. for C₁₆ H₂₇ ClN.sub. 2 O : C 64.3; H 9.11; Cl 11.86.Found: C 64.4; H 9.01; Cl 11.80.

EXAMPLE 12 Synthesis of 2-Cyclobutylamino-2',6'-acetoxylidide (CompoundK).

To a solution of cyclobutylamine (39.8 g) in 600 ml benzene was added2-chloro-2',6'-acetoxylidide (49.4 g), slowly, with stirring, and themixture was refluxed for about 5 hrs. After cooling, the mixture wasfiltered to remove the cyclobutylammonium chloride formed. The filtratewas stripped of solvent and excess amine in vacuo; leaving a cruderesidue.

The residue was dissolved in 0.5 M hydrochloric acid, the solution wasmade alkaline with sodium hydroxide solution and the base was extractedcarefully with ether. The ether solution was dried (Na₂ SO₄), the etherand low-boiling components were evaporated in vacuo at 40°-50°C and theresidue converted to a hydrochloride by addition of ethereal hydrogenchloride to its filtered ether solution. From the hydrochloride the basewas obtained by dissolution in water, addition of sodium hydroxidesolution to alkaline pH, extraction with ether, drying of the etherextract (Na₂ SO₄), filtering, and evaporation of the ether. The basecould be recrystallized from cyclohexane, petroleum ether (b.p.60°-110°C), or heptane. The melting point was found to be 75°-78°C.

Analysis: Calc'd. for C₁₄ H₂₀ N₂ O : C 72.4, H 8.68, N 12.06. Found: C72.4, H 8.88, N 11.93.

EXAMPLE 13 A. Synthesis of 2-(sec-butylamino)-2',6'-acetoxylidide

To a solution of 62.2 g of sec-butylamine in 500 ml benzene was addedslowly 41.5 g of 2-chloro-2', 6'-acetoxylidide. The mixture was heatedto reflux for seven hours and allowed to cool overnight. The precipitateof sec-butyl amine hydrochloride that formed was filtered off and thefiltrate was evaporated to an oily residue. The residue was dissolved inether, and the solution was filtered, dried (Na₂ SO₄), and evaporated toan oily residue (45.7 g). This crude product was distilled under vacuum,giving an oily liquid that solidified when chilled. Yield: 38.5 g (78%);b.p. 146°/0.05 mm; m.p. 44.5°-45.5°.

Analysis: Calc'd. for C₁₄ H₂₂ N₂ O : C 71.75, H 9.46, N 11.96. Found: C71.99, H 9.35, N 12.12. The hydrochloride melted at 176.5° - 178.5°.##SPC3##

B. Synthesis of 2-(N-ethyl-sec-butylamino)-2',6'-acetoxylidide (CompoundP)

To 140 g of diethyl sulfate was added 30.5 g of2-(sec-butylamino)-2',6'-acetoxylidide (made by the method described inthe first part of this example). The mixture was heated to 100°-110° forfive hours and cooled. Water and 5 N HCl were added to pH 2, forming asecond phase. After stirring, the aqueous phase (pH 2) was separated,washed with two 100 ml portions of ether and brought up to pH 9 withconcentrated NH₃. The basic aqueous phase was extracted with five 100 mlportions of ether. The solvent was stripped in vacuo from the combinedether phases, leaving a solidifying oil which was dissolved in ether,dried (Na₂ SO₄), filtered, and evaporated in vacuo. Yield: 26.2 g(76.8%); m.p. 50.5° - 54.5°. The product was twice distilled under highvacuum : b.p. 147°/0.025 mm; 165°/0.4 mm. Yield of redistilled product:21.4 g (62.7%).

Analysis: Calc'd. for C₁₆ H₂₆ N₂ O : C 73.23%, H 9.99%, N 10.68%. Found:C 73.06%, H 9.66%, N 10.47%.

We claim:
 1. An injectable local anesthetic composition havinglong-lasting local anesthetic effect which is a solution consistingessentially of a pharmaceutically acceptable carrier having dissolvedthereina. a non-heterocyclic aminoacyl anilide local anesthetic compoundin a concentration of from 0.05 to 5 percent by weight of the carrierand b. a toxin selected from the group consisting of from 0.5 to 10micrograms of tetrodotoxin per milliliter of the carrier and from 10 to20 micrograms of desoxytetrodotoxin per milliliter of the carrier. 2.The composition as defined by claim 1 wherein said component (b) istetrodotoxin.
 3. The composition as defined by claim 1 wherein saidcomponent (b) is desoxytetrodotoxin.
 4. The composition as defined byclaim 2 which further contains an effective amount of a vasoconstrictor.5. The composition as defined by claim 2 wherein said component (a) is2-(N-n-butyl-tert.-butylamino)-2',6'-acetoxylidide.
 6. The compositionas defined by claim 2 wherein said component (a) is2-(N-n-propyl-tert.-amylamino)-2',6'-acetoxylidide.
 7. The compositionas defined by claim 2 wherein said component (a) is2-(N-tert.-butylamino)-2',6'-acetoxylidide.
 8. The composition asdefined by claim 2 wherein said component (a) is2-(N-tert.-butylamino)-2',6'-propionoxylidide.
 9. The composition asdefined by claim 2 wherein said component (a) is2-(N-Ethyl-n-propylamino)-2',6'-butyroxylidide.
 10. The composition asdefined by claim 2 wherein said component (a) is2-Diethylamino-2',6'-valeroxylidide.
 11. The composition as defined byclaim 2 wherein said component (a) is prilocaine.
 12. The composition asdefined by claim 1 wherein said component (a) is lidocaine and saidcomponent (b) is tetrodotoxin.
 13. An injectable local anestheticcomposition having long-lasting local anesthetic effect which is asolution consisting essentially of a pharmaceutically acceptable carrierhaving dissolved thereina. lidocaine in a concentration of from 0.05 to5 percent by weight of the carrier and b. from 0.5 to 10 micrograms oftetrodotoxin per milliliter of the carrier.
 14. An injectable localanesthetic composition having long-lasting local anesthetic effect whichis a solution consisting essentially of a pharmaceutically acceptablecarrier having dissolved thereina. lidocaine in a concentration of from0.05 to 2 percent by weight of the carrier and b. about 1 microgram oftetrodotoxin per milliliter of the carrier.
 15. A method of inducinganesthesia in mammals, comprising administering to the mammal to beanesthetized an effective amount of an injectable local anestheticcomposition having long-lasting local anesthetic effect which is asolution consisting essentially of a pharmaceutically acceptable carrierhaving dissolved thereina. a non-heterocyclic aminoacyl anilide localanesthetic compound in a concentration of from 0.05 to 5 percent byweight of the carrier and b. a toxin selected from the group consistingof from 0.5 to 10 micrograms of tetrodotoxin per milliliter of thecarrier and from 10 to 20 micrograms of desoxytetrodotoxin permillimeter of the carrier.
 16. The method as defined by claim 15 whereinsaid component (b) is tetrodotoxin.
 17. The method as defined by claim16 wherein said component (a) is prilocaine.
 18. The method as definedby claim 16 wherein said local anesthetic composition further containsan effective amount of a vasoconstrictor.
 19. The method as defined byclaim 15 wherein said component (b) is desoxytetrodotoxin.
 20. Themethod as defined by claim 15 wherein said component (a) is lidocaineand said component (b) is tetrodotoxin.
 21. A method of inducinganesthesia in mammals comprising administering to the mammal to beanesthetized an effective amount of an injectable local anestheticcomposition having long-lasting local anesthetic effect which is asolution consisting essentially of a pharmaceutically acceptable carrierhaving dissolved thereina. lidocaine in a concentration of from 0.05 to5 percent by weight of the carrier and b. from 0.5 to 10 micrograms oftetrodotoxin per milliliter of the carrier.
 22. A method of inducinganesthesia in mammals comprising administering to the mammal to beanesthetized an effective amount of an injectable local anestheticcomposition having long-lasting local anesthetic effect which is asolution consisting essentially of a pharmaceutically acceptable carrierhaving dissolved thereina. lidocaine in a concentration of from 0.05 to2 percent by weight of the carrier and b. about 1 microgram oftetrodotoxin per milliliter of the carrier.
 23. The composition asdefined by claim 2 wherein said component (a) is2-(N-ethyl-iso-propylamino)-2',6'-propionoxylidide.
 24. The compositionas defined by claim 2 wherein said component (a) is2-methylamino-4'-(n-butoxy)-2',6'-dimethylpropion-anilide.
 25. Thecomposition as defined by claim 2 wherein said component (a) is2-(N-methyl-n-propylamino)-2',6'-butyroxylidide.